The production of crude oil from oleaginous matter, such as but not limited to soybeans, rapeseed, sunflower seed, peanuts, cottonseed, palm kernels, and corn germ, starts with the mechanical and thermal preparation of the oleaginous matter to remove external coverings and expose the cellular inner structure containing the oil. If the oil content of the oleaginous matter is less than typically 30% by weight, the prepared oleaginous matter goes directly to the solvent extractor in the form of a flake or pellet. If the oil content of the prepared oleaginous matter is greater than 30% by weight, a portion of the oil contained in the oleaginous matter is removed via pressure in a mechanical screw press and the pressed oleaginous matter goes to the solvent extractor in the form of a press cake.
The prepared oleaginous material in the form of flakes, pellets or cake is conveyed from the seed preparation process to the solvent extraction process and enters the solvent extractor where it is treated with an organic solvent, such as but not limited to n-hexane and its isomers, to solvent extract the oil.
Stationary screen, rotatable basket solvent extractors, (hereinafter “rotary extractor”) are well established in the art to perform the extraction of soluble substance contained in solid material such as for example the extraction of oil from oil bearing vegetable material.
For example, U.S. Pat. No. 2,840,459 discloses such a continuous solvent rotary extractor for the extraction of oils and soluble materials from solids by the use of liquid solvents. More particularly, it relates to an apparatus and processes in which extract-bearing solid material is moved substantially in a horizontal plane and successively supplied with solvent which percolates through the solid material and is drained into separate zones for recirculation and withdrawal. Still more particularly the relation of parts and steps may be so arranged that a substantially counter-current or any other character of movement between liquids and solids can be obtained.
Such rotary extractor is typically operated continuously. Accordingly, the material, previously prepared, is continuously introduced in the rotary extractor by pouring it from above into the basket (also called cells or chambers in the art) situated below a feeding point. The material continuously admitted and contained into the baskets, rotates, performing almost a complete revolution before the basket which is open at the bottom as well as at the top, moves into registry with an opening provided in the stationary screen bottom wall underneath the rotor. As the basket moves into registry with this opening, the spent material falls out through the latter. In-between the loading and unloading operation and thus during approximately 200 degrees circular revolution which the material performs with the rotor in its baskets, a solvent or miscella (the solution of the extracted substances in the extraction solvent) is admitted from above into the basket at one or several locations. The solvent percolates through, or alternatively fully immerses the material in the basket, dissolving soluble substances from the material, and drains by gravity through the stationary screen bottom underneath the rotor into collecting chambers from where the miscella is removed. In order to extract the desired component as completely as possible from the material, it is ordinary to expose the material to solvent or miscella at multiple extraction stages along the circular path. For example, it is known to introduce the miscella into the baskets in a “counter-flow” fashion such that the miscella is collected after it has percolated through the material to be extracted. The pure solvent is introduced at the last extraction stage along the circular path, while the more concentrated miscella drained from a basket at the first extraction stage along the circular path is collected and discharged to an evaporator or the like to effect isolation of the extracted material and recovery of the solvent which is recycled in a new extraction cycle. Once the extraction cycle has been completed, the extracted spent material is allowed to gravity drain and is collected and conveyed out of the system in order typically to be further processed and to recover the solvent which is recycled in the rotary extractor after adequate purification treatment. If the material is a vegetable oil bearing material such step typically involves a DTDC (Desolventiser Toaster Dryer Cooler).
Since the publication of U.S. Pat. No. 2,840,459, several design enhancements aimed at increasing the reliability, operability and performance of such rotary extractor have been disclosed. More specifically, those enhancements concerned the drive means for turning the rotor in order to improve the reliability, to avoid contamination and corrosion and to reduce power requirement. Material handling improvements reducing material obstruction issues were additionally disclosed.
U.S. Pat. No. 3,860,395 discloses a rotary extractor comprising a housing having a bottom floor provided with an opening; a star-shaped rotor turnable in said housing about a vertical axis and having a plurality of radial walls adjacent ones of which define respective extraction chambers which serially register with said opening in response to turning of said rotor; a ring-shaped rail fast with and surrounding said rotor within said housing for movement with said rotor, said rail having a radially outer upright circumferential surface portion; a plurality of shafts angularly spaced about said housing and each defining a fixed axis of rotation; a plurality of supporting rollers arranged interiorly of said housing each mounted on one of said shafts and being turnable about the respective fixed axis, said rail being supported on said rollers and the latter each having a flange extending transversely of the respective fixed axis of rotation and being located radially outwardly adjacent said circumferential surface portion so as to center said rail and thereby said rotor in said housing; journal means journalling the respective shafts and rollers for rotation and being wholly located exteriorly of said housing; and drive means for turning said rotor about said vertical axis, said extractor having no bearings located within the housing, and said rail and rollers being the sole support and centering means for the rotor.
U.S. Pat. No. 5,591,416 describes an improved rotating basket extractor having improved discharge means comprising a hopper section having a solid material entry and solid material exit end. The cross sectional area of the solid material entry end is smaller than the exit end so as to help prevent the agglomeration of solid material in the discharge hopper as it exits from the rotating baskets to a dual screw conveyor for subsequent travel to a discharge chute. The discharge hopper and the housing for the dual screw conveyor comprise slot means to provide for additional drainage of miscella therethrough. Additionally, the axially disposed rotatable shaft, supporting the rotating baskets, is journalled in a thrust bearing provided contiguous to the flooring substrate. Location of the thrust bearing there helps to minimize bearing contamination and corrosion.
U.S. Pat. No. 5,705,133 discloses a further improved rotating basket extractor of the type described in U.S. Pat. No. 5,591,416 in which power requirements are minimized through the combination of supporting the shaft by means of the single thrust bearing and driving the baskets by means of a bevel gear and pinion drive. Additional improvements help to prevent the solid material from obstructing miscella-carrying conduits.
The previous design enhancements were thus targeted for an increased operability and reliability of rotary extractor. Consequently higher uptime and reduced maintenance leading to higher productivity may be derived from those enhancements.
One of the parameters affecting the capacity of a rotary extractor processing a given material is the balance between the height of the bed of the material loaded in each basket and the time needed for the percolation of the solvent through such bed. Indeed, the expected capacity improvement coming from the increase of the height of the bed of the material is often eclipsed by longer drainage time of the miscella through such bed. This balance translates also in the number of baskets dedicated for the extraction and the number of baskets dedicated for ensuring enough drainage time. Drainage will be sufficient when enough miscella is removed from the spent material so it can be safely and economically further processed for example in DTDC equipment.
Practically sufficient drainage may demand about 15-20 minutes for a large rotary extractor. Accordingly several baskets will be dedicated in the drainage function and consequently, as the number of baskets making up the rotor is a constant, typically 18, fewer baskets will be available to perform an extraction function and the capacity of the rotary extractor will be reduced proportionally.
Accordingly, it remains a need in the art for the provision of an improved rotary extractor having a reduced drainage time. Such rotary extractor will have a higher capacity since the basket or baskets freed by the reduction of the drainage time will be available for an extraction function. Alternatively, such improved rotary extractor may also deliver the extracted spent material containing less residual miscella.